| Summary: | The geodynamic structure of the continental Northeast India (NEI) is shaped by the collision of the Indian and the Eurasian plate in the north and subduction of the Indian plate underneath the Burmese plate in the eastward direction. The oceanic lithosphere of the Bay of Bengal (BOB) is evolved due to rifting of India and Antarctica, has been mainly affected by two aseismic ridges emplacement: Ninetyeast and 85° ridges. Effective elastic thickness (Te) of the lithosphere is an important parameter for mechanical strength which provides information about the rheology of the deformation and evolution of the lithosphere. In this study region, we have calculated Te, by applying joint inversion of the real admittance and coherency between topographic and gravity anomaly data by using PlateFlex software. Load ratio (F) has also been determined to understand the mass distribution of surface and subsurface, where low F (< 0.2) in the Northeast India and the northernmost part of BOB represent surface loads is dominated in comparison to subsurface loads, while high F in the BOB region is dominated by subsurface loading. The spatial variation of Te varies ranging between 3–55 km. Low values of Te (9–16 km) over the 85° ridge correspond mainly to high thermal structure and weak lithosphere strength while slightly high in the activated Shillong Plateau (Te ~ 30 km) which indicates high seismic activity. High Te > 40 km in the Northeastern part of the Indian shield correlates mainly with low heat flow shows strong lithospheric strength.
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